1. Field of the Invention
The present invention relates generally to a magnetic memory device and a method of manufacturing the same, and more particularly to a magnetic random access memory (MRAM) and a method of manufacturing the same.
2. Description of the Related Art
In recent years, a variety of memories, which store data based on novel principles, have been proposed. Of these, there is known a magnetic random access memory (MRAM) making use of a tunneling magneto-resistive (TMR) effect, which was proposed by Roy Scheuerlein et al. An example of the MRAM including a so-called 1T1MTJ type memory cell (1T/1MTJ cell) is disclosed in “A 10 ns Read and Write Non-Volatile Memory Array Using a Magnetic Tunnel Junction and FET Switch in each Cell”, ISSCC2000 Technical Digest, p. 128.
As is described in this document, in the 1T1MTJ type MRAM, a conductor layer MX for electrically connecting one end of the current path of the transistor to the MTJ element is provided so as to project from the MTJ element. Consequently, the projecting region becomes a so-called dead space, and this is disadvantageous in miniaturization of memory cells.
There is a fabrication step in which a photoresist is coated on a projected shape that becomes an MTJ element and a pattern corresponding to the plan-view shape of the MTJ element is transferred onto the photoresist. In this step, due to optical characteristics, there is a tendency that the magnetic material shrinks in the longitudinal direction (easy-axis direction) of the MTJ element. As a result, the shape of the MTJ element differs from the target design, the target shape, and also the characteristics thereof differ from the estimated characteristics at the stage of design. For example, a difference in area leads to variation in resistance, variation in reverse magnetic field in a write mode, and variation in length in the longitudinal direction. Consequently, a stray magnetic field from the pinned layer would vary, and the reverse magnetic field in a “1” write mode and that in a “0” write mode would vary.